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How to Maintain Food Safety in a Dry Processing Environment

maintaining food safety in dry processing environment

What is a Dry Processing Environment?

A dry processing environment is a location where food materials are transformed into dry particles or where already dehydrated food products are further processed. For instance, this could involve turning a concentrated dairy formulation into powdered infant formula by spray drying or creating a pre-mixed spice blend by blending various dried spices. Dry processing generally refers to handling foods with low moisture content, such as cereals, animal feeds, grains, dried meats, or seeds. These types of food typically have a water activity (aw) of 0.85 or less, which denotes the amount of water available for chemical or microbial activity.

What is Water Activity (aw)?

grain processing factory dry environment
Water activity (aw) is a measure of the amount of water that is available for microbial and chemical reactions in a food product. It is defined as the ratio of the vapour pressure of water in a food sample to the vapour pressure of pure water at the same temperature and pressure. In simpler terms, water activity is a measure of how much “free” water is present in a food product, which can affect its shelf life and safety.
Water activity values range from 0 (completely dry) to 1 (pure water), with most microorganisms requiring a minimum water activity level of 0.91 for growth. Foods with a water activity level below 0.85 are typically considered low-moisture foods and are less susceptible to spoilage or microbial growth. Water activity is an important factor in the food industry, as it affects the shelf life, texture, and overall quality of food products.

Survival of Microorganisms in Dry Foods

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Although microorganisms typically require moisture to grow and multiply, they can survive and persist in dry foods until water becomes available. As such, dry foods are known to serve as a reservoir for foodborne pathogens, including Bacillus cereus in rice cereal, Clostridium botulinum in milk powder, or C. perfringens in spices, among others. 
The water activity (aw) level needs to be at 0.60 or lower to prevent microbial growth. However, it is important to note that food spoilage fungi and yeast can grow at low Aw levels of 0.60 to 0.70, although mycotoxin production cannot occur below 0.80. Therefore, it is crucial to implement robust monitoring procedures to prevent contaminated dry foods from entering processing environments. This is necessary to minimise the risk of foodborne illness outbreaks.

How Microorganisms Enter Dry Processing Environments

nuts in dry processing factory
Microorganisms can enter a dry processing environment through various means such as air circulation systems, rodents, and personnel’s clothing and shoes. 
It is crucial to maintain dry conditions to prevent the growth of microorganisms in dry processing environments since moisture can trigger their growth. Therefore, it is recommended to use “dry” methods for cleaning and disinfecting the processing area. These methods may include using vacuums, compressed air, or other dry cleaning techniques to remove dust and debris from surfaces and equipment. 
Furthermore, if liquid cleaning products are necessary, ensure they do not leave any water residue after use. In such circumstances, selecting “dry” cleaning products is advisable instead of liquid ones. This can help prevent the introduction of moisture to the processing environment, which could encourage microbial growth and increase the risk of food contamination. Proper cleaning and disinfection practices are essential to prevent the contamination of dry food products and ensure food safety.

Dry Cleaning Methods

dry cleaning in food processing factories

To prevent food safety hazards in dry processing environments, ‘dry’ cleaning has been proven effective, even though it may not provide an immaculate surface. This method can involve using brushes, scrapers, wiping, vacuum cleaner fittings, extraction tools, dry ice cleaning, or blowing with pressurised air. Gravity draining or pigging can also be used to remove products like cereals or grains. To ensure the cleaning tools are disinfected, a disinfectant solution, hot water, ovens, or steam can be used (> 80°C for bacteria and up to 120°C for spores). The tools must be dried thoroughly before returning to the dry processing environment. Note that ‘dry’ cleaning is only suitable for non-hygroscopic and/or non-sticky products.

Non-hygroscopic Materials

Non-hygroscopic refers to materials or substances that do not readily absorb moisture from the surrounding environment. In a dry processing environment, non-hygroscopic materials are preferred because they are less likely to support the growth of microorganisms. Some examples of non-hygroscopic materials include metals, plastics, and certain ceramics. In contrast, hygroscopic materials such as paper, cardboard, or some fabric types can absorb moisture and create a more hospitable environment for microbial growth.

Gravity Draining and Pigging

wet cleaning of food processing factory

Gravity draining and pigging are two methods of removing leftover material from processing equipment. Both gravity draining and pigging are used in the food processing industry to remove product residue from equipment, which can help prevent cross-contamination and ensure the quality and safety of the final product.

Gravity Draining

Gravity draining involves allowing a product to flow out of equipment using gravity, which can be effective for non-sticky products like grains and cereals. This method is simple and doesn’t require any additional equipment, but it can be slow and may not remove all traces of the product.


Pigging, on the other hand, involves using a cylindrical object (called a “pig”) that fits snugly inside the processing equipment and is pushed through with compressed air, water, or another liquid. The pig scrapes the sides of the equipment, pushing any remaining product out ahead of it. This method is effective for both non-sticky and sticky products and can remove more products than gravity draining. However, it requires more equipment and can be more time-consuming.

Dry vs. Wet Disinfection Methods

dry processing environment cleaning
To prevent the introduction of microorganisms into the processing environment, it is important to regularly disinfect food contact areas. However, wet disinfection can cause a loss in productivity as the surface needs to completely dry before production can resume. Dry disinfection is therefore preferred and can be achieved through various methods, including wiping or spraying with alcohol-based disinfectants like isopropyl alcohol-quats mixture, applying dry heat, or using gaseous antimicrobial agents such as ethylene oxide, hydrogen peroxide vapour, ozone, or chlorine dioxide. Wet disinfection should only be utilised as a last resort or performed infrequently to avoid introducing moisture into the environment.
The key takeaway is to maintain the principle of keeping dry things dry. Businesses can reduce production downtime and conserve water by implementing dry cleaning and disinfection procedures. When managed effectively in dry processing environments, cleaning and disinfection practices can significantly decrease the risk of food safety hazards.

Conclusion: Dry Processing Environment Food Safety

In conclusion, a dry processing environment is a place where food materials are transformed into dry particles or where already dry food products are further processed. Low-moisture foods’ water activity (aw) level is an essential factor affecting their shelf life, texture, and overall quality. The survival of microorganisms in dry foods can be a potential risk to food safety, and proper cleaning and disinfection practices are essential to prevent contamination. Dry cleaning has been proven to be an effective strategy to prevent food safety hazards in dry processing environments. It involves various methods such as vacuuming, brushing, pigging, or wiping with pressurised air to remove leftover material from processing equipment. By implementing good hygiene practices, companies can ensure that their dry food products are safe for consumption and maintain their quality and shelf life.

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